Method of producing fluorescent screens



Oct. 24, 1950 J. JOHNSON 2,527,134

METHOD OF PRODUCING FLUORESCENT SCREENS Filed Nov. 14, 1947 2 Sheets-Sheet 1 PREPARE BUL 8 APPLY AND DISTRIBUTE BINDER 7'0 SCREEN AREA IN TRODUCE RE TE N 77 V5 PHOS PH 0R DRY BY WARM AIR FLOW APPLY AND DISTRIBUTE BINDER IN TRODUCE ACTINIC PHOSPHOR DRY BY WARM AIR FLOW APPLY GRAPH/TE AND ALUMINA RING APPLY SEAL ms BINDER FIG. 3

an KE /N VE N TOR J. B. JOHNSON A T TORNEY Oct. 24, 1950 J. B. JOHNSON METHOD OF PRODUCING FLUORESCENT SCREENS 2 Sheets-Sheet 2 Filed Nov. 14, 1947 //v l EN TOR J. B. JOHNSON A 7' TORNEV 5103. wmawwwmm k3 E Patented Oct. 24, 1950 METHOD OF PRODUCING FLUORESCENT S CREEN S John B. Johnson, Maplewood, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, Y., a corporation of New York Application November 14, 1947, Serial No. 785,935

4 Claims. (Cl. 117-335) This invention relates to the manufacture of cathode-ray tubes and more particularly to methods of producing fluorescent screens for such tubes. I

One object of this invention is to facilitate the manufacture of a revolving screen type cathoderay tube for the visual representation of waves, such as disclosed in J. B. Johnson Patent 2,324,089 of July 13, 1943, for Electron Discharge Apparatus.

Another object of this invention is to improve fluorescent coatings for electronic devices and more particularly such coatings of the cascade type and included in revolving screen cathoderay tubes.

The presently known methods of applying fluorescent materials in the stationary types of cathode-ray tubes cannot be used in the manufacture of revolving screen type cathode-ray tubes be cause of the shape of these tubes in which the fluorescent material must be applied to the inner surface of a cylindrical side wall portion of the tube.

A feature of the invention relates to a process for producing a fluorescent screen upon the inner wall of a cylindrical portion of a revolving screen type cathode-ra tube in which centrifugal forces of revolution assist in spreading the coatings uniformly over the inner surface of the tube and embedding the fluorescent material in the fluid binder coatings.

Another feature relates to a method of electrically connecting conductive, for example graphite, coatings on the inner surfaces of two spaced, for example end, portions of a cathode-ray tube.

A further feature relates to a coating of refractory material as a ring on the inner surface of a portion of the cathode end of a revolving screen type cathode-ray tube.

The invention and the above noted and other features thereof will be more fully understood from a consideration of the embodiment illustrated in the accompanying drawings in which:

Fig. 1 is an elevational view of a completed revolving screen type cathode-ray tube;

Fig. 2 is a perspective view of a part of a revolving screen type cathode-ray tube and the apparatus utilized in the production ofthe fluorescent coating therein in accordance with features of this invention.

Fig. 3 is a cross-sectional View of a hypodermic syringe fitted with an extension tube for inject: ing fluid binder into a revolving screen type cathode-ray tube; and

Fig. 4 is a chart of the steps in the process of coating the interior surface of a revolving screen type cathode-ray tube.

Referring now to the drawings, a revolving screen type cathode-ray tube illustrative of one embodiment of this invention, is shown including a cylindrical wall 2 upon which the fluorescent screen is to be formed, dome-shaped ends 3, 4, cathode tubulation 5 and anode stem 6. Tube l preferably consists Of a glass bulb of generally spherical shape about ten inches in diameter. The screen forms a cylindrical band about two and one-half inches wide upon the inner surface of the cylindrical wall '2 of tube I. The completed tube is about twenty inches long from the end of the cathode tubulation 5 to the end of the anode stem 6.

The steps in the manufacture of a revolving screen type cathode-ray tube shown in Fig. 4 include preparation of the tube by annealing, washing, drying and applying silver paste to form a line i on the inner surface of the tube in a plane that includes the axis of the tube, from a point 8 on dome-shaped end 3 to a point 9 on domeshaped end 4 followed by baking the tube in a radiant heat oven to dry the silver paste. The baking includes raising the temperature of the tube graduall to about 360 C., holding this term perature constant for about 15 minutes and then permitting the tube to cool to room temperature.

The function of this silver line 1 is to provide an electrical connection between the conductive, for example graphite, coatings that are applied to the inner surface of the dome-shaped end portions of the tube in a subsequent step in the manufacture of the tube.

The succeeding steps in the manufacture of the tube during which the fluid binder, fluorescent material, graphite and alumina coatings are applied to the inner surface thereof take place while the tube is revolved about its axis in a lathe as shown in Fig. 2, in which a three-jawed chuck 20 grips the cathode stem 5 0f the tube l with the axis of tube l coincident with the axis of revolution of chuck 20. Chuck 20 is rigidly attached to a rotatable hollow shaft 2i which is supported by two bearings 30, 3| on stanchions 32, 33 mounted on bench 34. Shaft 2! is rotated by motor 35 which is mounted on bench 3 and which has a pulley 36 that drives pulley 31 on shaft 2] by a belt 38. Bracket 39, also mounted on bench 4, has three rollers Ml equally spaced around the axis of revolution of lathe shaft 2|, only two of the rollers being visible in Fig. 2. 301 .15 4 su port anode stem 6 of tube I by con- 3 tact with cylindrical neck 4| thereof as a threepoint bearing while the tube revolves.

While the tube is revolved at about revolutions per minute, about two cubic centimeters of a first fluid binder are injected into tube I through the open end 42 of anode stem 6 by means of hypodermic syringe 10 shown in Fig. 3. Syringe ID has a metal extension tube H with its tip end bent normal to the main body thereof and terminating in a hypodermic needle 12. The fluid binder preferably consists of five parts by volume of ethyl silicate, two parts formic acid solution and one part absolute ethyl alcohol. After the fluid binder is injected by means of syringe 10, the extension tube 1| thereof is withdrawn from tube A small brush is then inserted through open end 42 of tube and is used to spread the fluid binder evenly over the inner surface of cylindrical wall 2 of tube I while the tube is revolving. The centrifugal action of the revolving tube assists in spreading the fluid binder into a uniform coating on wall 2.

Immediately following the spreading of the fluid binder over the inner wall 2, the nozzle of insufliator 5| is inserted into tube I through open end 42 thereof. Insufflator 5| includes a glass upper portion 52 and a glass lower portion 53 which are held together by an air-tight connection composed of rubber sleeve 54. The bottom portion 53 contains about three cubic centimeters of yellow phosphor fluorescent material which was placed therein previously. This fluorescent material preferably is composed of a mixture of about 84 per cent zinc sulphide, 16 per cent cadmium sulphide, activated by copper of an amount in the order of 0.01 per cent or less. Tube 55 is connected to a source of low pressure filtered air. The lower end of nozzle 50 is covered with a fine mesh gauze. Glass tube 56 of insufliator 5| enters lower portion 53 through a sealed opening and end 51 is formed downward normal to the body of tube 56 and is drawn down to form a small opening at the tube end. Glass tube 58 enters the glass upper portion 52 of insufliator 5| through a sealed opening and end 50 thereof is formed upward and drawn down to form a small opening at the tube end at a small distance from the junction SI of glass tube 62 and upper portion 52 of insufilator 5|. Tube 63 opens into tube 58 and is sealed thereto. Tube 6| connects with tube 56 through flexible tube 64. The lower end of tube 65 opens into tube 58- and is sealed thereto. The upper end of tube 65 is open.

When a source of low pressure air is connected to tube 55, air will flow from the upper end of tube 65 which acts as a by-pass and allows only a slight amount of air to escape at the lower end of tube 51 Or the upper end of tube 60. When the upper end of tube 65 is closed, as for example, by placing a finger over it, the air pressure causes a considerable increase of air flow through the lower end of tube 51 and the upper end of tube 60. The air flow from the lower end of tube 51 will agitate the fluorescent material in lower portion 53 into a dust cloud within the insufiiator body and the air pressure from the upper end of tube 60 will blow the fluorescent material through tube 62 and into the interior of tube I through the fine mesh gauze on the end of nozzle 50 causing a cloud of fluorescent material within tub The fluorescent material in the dust cloud gradually settles upon the inner surface of tube to form an evenly spread coating which adheres to the previously applied fluid binder, The centrifugal force of the revolving tube imbeds the particles of the fluorescent material into the wet fluid binder.

The fluid binder is now dried by passing a flow of warm air at about 10 C. above room temperature for about 15 minutes through tube This air is warmed in heater unit shown in Fig. 2 in which a glass cylinder BI is supported on bench 34 by bracket 82. Cylinder 8| has removable end plugs 83, 84. A tube is inserted through end plug 84 and connects a source of low pressure dry air into cylinder 8|. A tube 86 inserted through end plug 63 terminates at one end within cylinder 8| and at its other end within hollow shaft 2|. Heater coil 81 is located within heater cylinder 8| and is connected to a source of electric power through cord 88 which passes through end plug 84. The flow of air entering through tube 85 passes through hollow shaft 2| into tube and exhausts at open end 42 thereof.

Following this drying operation, a second fluid binder consisting of about 2.3 cubic centimeters of the sam silica solution used as the first fluid binder is injected into tube upon the inner surface of cylindrical wall 2 thereof by means of syringe l0 and is spread evenly over wall 2 by means of syringe 10. The centrifugal action of the revolving tube assists in spreading this fluid binder evenly into a uniform coating on wall 2. Immediately thereafter about 2.3 cubic centimeters of actinic phosphor fluorescent material is injected into the interior of tube by means of insufflator 5| and allowed to settle upon the surface of the coating of the second fluid binder. This fluorescent material preferably is composed of zinc sulphide activated by a mixture of copper and silver of an amount in the order of 0.01 per cent or less, The centrifugal force of the revolving tube imbeds the particles of this fluorescent material into the second fluid binder. The second fluid binder is then dried by blowing warm air at about 10 C. above room temperature through tube by means of heater unit 80 for about 15 minutes. The rotation of tube is then stopped and tube is removed from the lathe.

- Any loose fluorescent material within tube is removed by slapping the wall of tube with the flat of the hand to shake loose any poorly adhering material and then blowing any loose material oif the interior wall with a gentle jet of air.

The amounts of the fluid binders and fluorescent materials depend upon the area of surface to be covered. In the preferred form of tube described herein the area of the fluorescent screen is about 500 square centimeters. Two cubic centimeters of the materials deposited evenly on this area will result in a coverage of about 0.004 cubic centimeter per square centimeter of surface, 2.3 cubic centimeters of material will result in a coverage of about 0.0046 cubic centimeter per square centimeter of surface and 3 cubic centimeters will result in a coverage of about 0.006 cubic centimeter per square centimeter of surface.

Tube is again placed in the lathe and revolved at about 10 revolutions per minute. A flow of air of about two cubic feet per minute about 10 C. above room temperature is now forced into tube I through heater unit 80. A coating comprising a colloidal suspension of graphite is evenly applied by brush to the inner surface of dome-shaped ends 3, 4 of tube from the edges of coating of fluorescent material on wall 2, but not covering the fluorescent material, the graphite coating extending from the fluorescent coating over the dome-shaped ends 3, 4 to points |2 of tube I,

rem ss.

A coating consisting of a mixture oflevigate'd alumina, 'amylacetate andfa red dye isthen'applied as anarrow'ring I3 onthe inner s urfaceof cathode tubulation 5 by meansoffia brushjdipped inthemi igure. Ring'13' is apartfr'om th raphite coatingybeing separated therefrom b coated'ring f'lk about.one=eighthjinchjwid sealing binder composed 'of about' four u'bi' timeters of; the same silica "solution used as; first andse'cond binders is nowinj ected into tube I upon the cylindrical wall 2 by means of syringe I and spread therewith evenly over cylindrical wall 2 and overlapping about one-quarter inch on the graphite coating on dome-shaped ends 3, 4. The centrifugal force of the revolving tube assists in spreading this fluid binder evenly into a uniform coating. This binder is allowed to dry and then the revolution of tube I is stopped and the tube I is removed from the lathe chuck 2%.

The function of the ring I3 of alumina around the inner surface of the cathode tubulation 5 is to provide a rough surface which will break up any getter material which reaches this part of the tubulation during the subsequent gettering operation in the manufacture of the tube, and,

coatings and to dry and harden the several coatings. The tube I is placed in a ring stand in a radiant heat oven with the axis of the tube I vertical with its ends open. The oven temperature is gradually raised so that a temperature of about 500 C. is reached at the end of an hour and this temperature is held constant for about 45 minutes while a circulation of air is forced through the oven and then the oven is permitted to cool. Tube I may be withdrawn from the oven when the oven temperature is reduced to about 100 C. Tube I is then ready for the further steps in its manufacture including the application of the cathode and anode stem devices.

While this invention has been disclosed with reference to a specific embodiment, it is to be understood that it is to be considered as limited in scope by the appended claims only.

What is claimed is:

1. The method of forming a fluorescent screen upon the inner surface of a cylindrical wall of a transparent hollow glass vessel which comprises continuously revolving said vessel about a horizontal axis coincident with the longitudinal axis of said cylindrical wall at a rate to produce substantial centrifugal forces, introducing a first fluid binder comprising a mixture of ethyl silicate, formic acid and absolute ethyl alcohol into said vessel, brushing said binder evenly over said wall, injecting a cloud of yellow phosphor fluorescent material into said vessel in proximity to said wall, allowing said material to settle on said binder and to be embedded therein by centrifugal force, drying said binder by a flow of warm air at about 0. above room temperature for about minutes, introducing a second fluid binder comprising said mixture into said vessel, distributing said second binder evenly over the yellow phosphor fluorescent material on said wall, injecting a cloud of blue actinic phosphor fluorescent" material into'said vessel in proximity to said wall} allowing said actinic material to settle on thesecond binder, and'flnally drying-said'second fluid binder; by aflow of warm air at about 10 Cfabove room temperature for about 15 minutes. i p

2. The method of manufacturing a hollow 'glass vessel' having a cylindrical wall portion, two dome-shaped end portions and a 'cathode eo s rs e sa zd meis aned end tions, which comprises drawing a line with con,- ductiveflpaste between said dome-shaped. end portions on the inner" surface of'the vesse'l','fh'eat- 'ing" said vessel to dry said paste, continuously revolving said vessel about an axis coincident with the axis of said cylindrical wall portion of said vessel, coating the inner surface of said cylindrical wall portion of said vessel with a fluid binder, injecting a cloud of fluorescent material into said vessel in proximity to said wall, allowing said material to settle on said binder, drying said fluid binder, coating the inner surfaces of both dome-shaped end portions of said vessel with a conductive material overlapping the end portions of the dried conductive paste line, coating the inner surface of said cathode tubulation of said vessel with a ring of refractory material in suspension adjacent to but apart from the conductive coating of the adjacent dome-shaped end portion of said vessel, and finally baking said vessel to dry said coatings.

3. The method of manufacturing a hollow glass vessel having a cylindrical wall portion and two dome-shaped end portions, which comprises drawing a line with silver paste between said dome-shaped end portions on the inner surface of said vessel, drying said silver paste, continuously revolving said vessel about an axis coincident with the axis of said cylindrical wall portion of said vessel, coating the inner surface of said cylindrical wall portion of said vessel with a fluid binder, injecting a cloud of fluorescent material into said vessel in proximity to said wall, allowing said material to settle on said binder, drying said fluid binder, coating the inner surfaces of said dome-shaped end portions of said vessel with a colloidal suspension of graphite covering the end portions of said line of silver paste, and finally baking said vessel to dry the coatings.

4. The method of manufacturing a hollow glass vessel having a cylindrical wall portion, two dome-shaped end portions and a cathode tubulation on one of said dome-shaped end portions, which comprises drawing a line with silver paste between said dome-shaped end portions on the inner surface of said vessel, drying said paste, continuously revolving said vessel about a, horizontal axis coincident with the axis of said cylindrical wall portion of said vessel, coating the inner surface of said cylindrical wall portion with a fluid binder comprising ethyl silicate, formic acid and absolute ethyl alcohol, injecting a cloud of yellow fluorescent material into said vessel in proximity to said wall, allowing said material to settle on said binder, drying said binder, coating said yellow fluorescent material with said fluid binder, injecting a cloud of blue actinic fluorescent material into said vessel in proximity to said wall, allowing said blue actinic fluorescent material to settle on said last-mentioned coating of binder, drying said last-mentioned coating, coating the inner surfaces of both dome-shaped end portions of said vessel with a, colloidal suspension of graphite covering Number Name Date the end portions of said line of silver paste, and 2,066,592 Wadsworth Jan. 5, 1937 finally baking said vessel to dry the coatings. 2,243,828 Leverenz May 27, 1941 2,252,552 Calbick et a1 Aug. 12, 1941 JOHN B. JOHNSON. 5 2,318,060 Cortese May 4, 1943 2,324,089 Johnson July 13, 1943 REFERENCES CITED 2,329,632 MarSden, Jr. Sept. 14, 1943 The following references are of record in the 21336346 Marden at 1943 file of patent: O 1 10 2,435,436 Fonda Feb. 3, 1948 UNITED STATES PATENTS Number Name Date 1,495,487 Johnson May 27, 1924 2,032,761 Marsden Mar. 3, 1936 

